A conventional railroad monitoring system relies on a wired sensor monitoring technology, and, thus, it is limited in that it does not guarantee reliability and stability during maintenance and management. In particular, it is difficult to access components in a truck and a running gear of a railroad vehicle, and installation of a wired sensor therein is limited. Therefore, it is difficult to acquire real-time monitoring data of main devices of the railroad vehicle.
In this regard, Korean Patent Laid-open Publication No. 10-2009-0056086 (entitled “System and method for monitoring safety of railroad facilities”) discloses a system and method for monitoring safety of railroad facilities, including: multiple sensor nodes installed in the railroad facilities to detect a status of the railroad facilities and configured to perform a signal process to the railroad facility status detection information by near field communication and transmit the railroad facility status detection information; a sink node device configured to collect the railroad facility status detection information from each sensor node and transmit the railroad facility status detection information; a gateway configured to receive the railroad facility status detection information transmitted from the sink node device and perform a signal process to the received detection information by mobile communication; and a control server configured to receive the railroad facility status detection information from the gateway, output the received detection information and store the received detection information in a memory area, check a value of the received railroad facility status detection information, and output a warning message and a warning sound warning about safety abnormality of the railroad facilities when the checked value exceeds a predetermined reference value.
Such a conventional railroad monitoring system diagnoses a failure according to status detection information detected by a sensor installed at a railroad facility on the ground or in a maintenance depot. Accordingly, it is possible to diagnose a status of a railroad vehicle only at a limited location where the sensor is installed. Further, reliability of the diagnosis is low, and it is possible to diagnose only after any failure occurs. Furthermore, a failure cannot be predicted or suppressed by monitoring a status of the railroad vehicle in real time. In order to solve such a problem, a study on a method for combining a wireless sensor configured to monitor an operation status of each component in a railroad vehicle is being conducted. Further, in order to readily supply power to the wireless sensor, a study on a self-generation module configured to use various energy sources present in the railroad vehicle is also being conducted.
Energy harvesting is one representative technology for the self-generation module. The energy harvesting refers to a technology of harvesting or scavenging discarded energy from the environment and converting the energy into usable electric energy. According to the energy harvesting, natural light energy, low-temperature waste heat energy from a human body or a combustion engine, micro-vibration energy from a device mounted on/attached to a portable device, dissipation energy caused by human physical activities, and the like can be absorbed and converted into electric energy. Further, the energy harvesting may use energy harvesting elements such as a thermoelectric element, electrochemical reaction, a DC/AC generator, a piezoelectric transducer, a capacitor transducer, a photovoltaic cell, and the like. Generally, power obtained by the energy harvesting is approximately in the range of microwatt (μW) to milliwatt (mW).
Such energy harvesting can be applied to various fields. By way of example, vibration generated in a railroad vehicle or a car driving at a high speed can be utilized by using the energy harvesting, so that electric energy can be produced.
In this regard, Korean Patent Laid-open Publication No. 2013-0011471 (entitled “Broadband energy harvesting apparatus using a multi-degree-of-freedom vibrating body”) discloses a technology for efficiently obtaining electric energy in a wide frequency range by vibrating a rigid body with a multi-degree of freedom to cause multiple natural frequencies to appear close to each other and thus widening a resonant frequency band with respect to external vibration.
However, the above-described conventional technology does not give consideration to both of vibration frequencies in high-speed and low-speed periods, and, thus, is limited in widening a power generating frequency band.
Meanwhile, a wireless sensor configured to monitor a status of various systems, such as a train operating system, a high-pressure system, a traction system, a braking system, an auxiliary power supply, and an in-vehicle electric device, included in a railroad vehicle can be combined with the railroad vehicle, and information sensed by the wireless sensor can be transmitted through a wireless communication path. In this case, wireless communication of the wireless sensor can be processed by using energy acquired by energy harvesting.
In this regard, U.S. Patent Laid-open Publication No. 2012-0255349 (entitled “Micro-power systems”) discloses a technology of producing and managing energy using an energy harvesting structure attached to a vehicle and utilizing the produced and managed energy as electric power for operating a module for RF communication.
However, a railroad vehicle or a car driving at a high speed or a machine generating severe vibration generates severe vibration or high-temperature heat. Thus, reliability cannot be guaranteed during data transmission for wireless communication according to the above-described conventional technology.